Currently, a structure of a mobile communication network is shown as FIG. 1; under the network structure, a data flow of a mobile user has to access Internet via an access network and a core network.
With abundant terrestrial transmission and a growing decrease in a transmission cost, a demand for traffic of the Internet and a requirement on a time delay of the Internet has been improved continuously, and a new networking mode is forming. FIG. 2 shows a structural diagram of a possible offloading networking; under the networking structure, a mobile user can either connect to the Internet via a core network by a traditional channel, or directly access the Internet from an access network through performing offloading at an IU interface (interconnection point between a Radio Network Controller (RNC) or a Base Station Controller (BSC) and a 3G core network, specifically referring to an interface between a 3rd wireless communication access network and a core network), thus achieving a higher data flow speed and a lower cost.
At present, this solution is still being argued by the 3rd Generation Partnership Project (3GPP), and related protocols have not yet been determined.
There are two offloading solutions for the IU interface in the 3GPP, one of which is to deploy a Gateway General Packet Radio Service Support Node (GGSN) on an RNC and the other one of which is to deploy a Network Address Translation (NAT) device on the RNC.
The main features of the NAT solution are as follows: between the RNC and a core network, an offloading device judges whether a data flow needs offloading by means of monitoring a Non-Access Stratum (NAS) message and parsing information related to a Packet Data Protocol (PDP) in the NAS message, performs NAT for an original data flow if the offloading is needed, and then directly pushes the data flow to an Internet access point. The offloading judging method has the following disadvantages:                (1) information obtained in a monitor mode is incomplete, it is possible that a NAS message cannot provide complete user information, and offloading characteristics for distinguishing users cannot be provided; and        (2) the offloading judging method is separated from a Quality of Service (QoS) strategy of a core network, and operators may have to define two QoS strategies, thus bringing difficulty for management.        